1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus having the zoom lens, and is suitable to an image pickup apparatus such as a digital still camera, a video camera, and a silver-halide film camera.
2. Description of the Related Art
Since single-lens reflex cameras of recent years have a moving image photographing function, these cameras are required to have improved focus tracking performance for a moving image being recorded for video and to suppress noise such as a motor sound made by driving lenses.
For example, the contrast-detect automatic focus which determines the in-focus state based on the contrast of the image being recorded executes a wobbling operation for slightly moving a focus lens unit of a photographic optical system forward and backward to determine the peak of the contrast. To shorten the time required to execute the wobbling operation of the focus lens unit and to reduce the motor sound associated with the wobbling operation, it is important to make the focus lens unit more compact and lighter.
On the other hand, the photographic optical system with an image shake correction function is required to be highly responsive to an image shake and to suppress noise such as a motor sound made by driving lenses. Therefore, it is also important to make an image stabilization lens unit of the photographic optical system more compact and lighter.
U.S. Pat. No. 7,382,550 discusses a zoom lens which includes, in order from an object side to an image side, a first lens unit having negative refractive power, a second lens unit having positive refractive power, a third lens unit having negative refractive power, and a fourth lens unit having positive refractive power. This zoom lens realizes a more compact and lighter image stabilization lens unit by employing a single lens of the second lens unit as the image stabilization lens unit. However, since the zoom lens employs a first lens unit including a plurality of lenses of large lens diameters as the focus lens unit, the zoom lens still has an insufficiently compact and light focus lens unit.
U.S. Pat. No. 8,189,074 discusses a zoom lens which includes, in order from an object side to an image side, a first lens unit having negative refractive power, a second lens unit having positive refractive power, a third lens unit having positive refractive power, a fourth lens unit having negative refractive power, and a fifth lens unit having positive refractive power. This zoom lens realizes more compact and lighter focus lens unit and image stabilization lens unit by employing the second lens unit and the fourth lens unit, both of which have relatively small lens diameters and light weights, as the focus lens unit and the image stabilization lens unit, respectively. An aperture stop is arranged at an object side of the fourth lens unit, which is the image stabilization lens unit, and the aperture stop, which tends to be larger because of its drive unit, and the image stabilization lens unit are arranged side by side at the image side of the zoom lens. Therefore, the zoom lens tends to be larger to reserve a space for these components. Particularly in an interchangeable lens for a single-lens reflex camera, amount for detaching, a mirror in the camera, and the like are arranged at the image side, and therefore, it is difficult to reserve a space for arranging the image stabilization lens unit and the aperture stop.
Generally, the focus lens unit and the image stabilization lens unit may each include a lens unit having a less number of lenses to be more compact and lighter. However, when the numbers of lenses constituting the focus lens unit and the image stabilization lens unit are simply reduced, aberrations remaining in the focus lens unit and the image stabilization lens unit increase and, as a result, aberration variation due to the focus and the image stabilization increases. Therefore, it is important to appropriately set the refractive powers of the focus lens unit and the image stabilization lens unit as well as the arrangement of these units in the entire zoom lens to make the focus lens unit and the image stabilization lens unit more compact and lighter while improving their optical performance.